Common Names

Flocculent flax scale, Flax scale

Biostatus and Distribution

This distinctive endemic scale insect lives on the underside of leaves of its endemic host plants, especially New Zealand flax, Phormium species (Hemerocallidaceae). It is found on the North and South Islands.

Conservation status: Widespread in the North and South Islands on its host plants in native ecosystems and in gardens and parks.

This scale insect breeds all year. There do not appear to be discrete generations. It is not known how long it takes from birth to adult. All stages live on the underside of host plant leaves, often in large groups.

The bright yellow body of the mature female insect lives under a white wax scale cover that is often coated with white flocculent wax when immature. Bright yellow eggs are laid in the posterior space under the scale cover. The body shrinks as eggs are formed. After the first instar (stage) nymphs hatch, they leave the female scale through a flap at the posterior end of the scale. The crawlers walk over the plant leaf and settle in a place to feed. The scale insect spends the rest of its growth and development in this place. Only the adult male can move away. Once settled the nymph forms a wax cover. The wax scale cover is coated with flocculent wax. The first instar scale moults (changes skin) into the second instar. Unlike other scale insects, it incorporates the first instar skin and scale cover into its enlarged scale cover. The scale cover of the second instar scales are also coated with flocculent wax. When the female second instar moults into the third instar scale, it also incorporates the second instar skin and scale cover into its scale cover. The new part of the last stage female scale colour is pale to light gold in colour. The third instar female grows into the mature female that is receptive to the male and lays eggs after mating.

When the second instar male has finished feeding and grown to full size, it moults into a non-feeding prepupae that stays under the same second instar scale cover. Likewise, when the prepupae moults into the pupa, it to stays under the same scale cover. The pupa moults into the adult male which is coloured red and has legs, one pair of wings and a long pointed abdomen. When its body has hardened, it backs out of the scale cover and goes in search of mature female scales with which to mate.

FeedingAdult females and juvenile scales have sucking mouthparts. Specially shaped long rods called stylets are used for feeding. Until used for feeding the tips of the stylets held in the short sheath-like rostrum. When it wishes to feed, the scale insect moves the tip of the rostrum onto the surface of the plant. The stylets are then gradually pushed into the plant and manoeuvred into cells of the plant. The stylets form two tubes, one down which saliva is pumped into plant cells and the second tube through which it sucks the contents of the plant cells. The dead plant cells turn yellow and the yellow patches of dead cells can be seen on the upper side of plant leaves. Unlike other scale insects (Coccoidea), Diaspididae scale insects possess a blind gut with no connection between the stomach and the anal opening.

Walking, flying and dispersalThe crawler stage of the first instar nymph and the adult males are the only two stages with functional legs. They both have three pairs of legs and antennae. The adult male also has one pair of wings. The crawler is the main stage for dispersal. Most crawlers walk to a place on the same leaf, but some travel to other leaves on the same plant. Some crawlers disperse to other plants; most distance dispersal is by air. It is not known if crawlers of this species go to high points of the plant and stand up to catch the wind. Adult males can walk over a leaf and colony in search of females with which to mate. They can also fly to nearby colonies, and may be carried further by wind.

Recognition

The clusters of white flocculent wax on leaves of host plants make the recognition of these colonies of Flocculent flax scale easy. Single scales can be confused with other species of white Diaspididae found on flax and cabbage trees; usually there are some scales with flocculent wax to enable identification. The presence of chlorotic, yellow, areas on the upper side of leaves usually indicates the presence of Diaspididae scales on the underside of leaves.

One of the three other native Diaspididae on flax is an unnamed species, Leucaspis sp. 1 that is usually only found in the groove on the upper side of leaves. A fungal infection often indicates the presence of this species of scale insect. Another native white scale insect that may be seen on flax and cabbage trees is the Cordyline scale, Anzaspis cordylinidis. These are long, narrow scales that may have a dark or pale cap and can occur on either side of leaves. A second species of Leucaspis has also been found of flax leaves. It is wider than A. cordylinidis and the female has a dark scale cover under the white wax.

On leaves of Cabbage trees, Cordyline species, two other species of white scale may sometimes be found, Waratah scale, Pseudaulacaspis brimblecombei Williams, 1973, and White palm scale, Pseudaulacaspis eugeniae (Maskell, 1892). The mature female scales are similar in shape to Flocculent flax scale, but no life stage produces flocculent white wax.

Sometimes old colonies and declining colonies of Flocculent flax scale are occupied by mealybugs (Pseudococcidae). Mealybugs secrete honeydew that may result in sooty mould fungi. Diaspididae scale insects do not secrete honeydew.

Natural Enemies

ParasitoidsOne wasp parasitoid has been found. The tiny female wasp parasitoid lays an egg in a scale insect. The wasp larva lives in the scale body. When it is fully grown it leaves the body and pupates under the scale cover. The adult wasp chews a hole in the scale cover in order to get out.

PredatorsTwo ladybirds and caterpillars of one moth predate on Flocculent flax scale. The caterpillars form webbed tunnels in the scale insect colonies. They hide in the tunnels by day and come out to feed on the scale at night. When fully grown the caterpillar spins a cocoon in its tunnel and changes into a pupa from which the moth later emerges.

The steelblue ladybird feeds on a variety of insects including scale insects. The endemic ladybird, Rhyzobius sp. Is only known to feed on Flocculent flax scale. Both adults and larvae feed on the scale insect.

Saprophagous fungusA brown saprophagous fungus, Ramichloridium punctatum, may be found on dead scale insects. The fungus is not believed to kill the scale insects.

Host Plants

The Flocculent flax scale is most commonly found on the underside of leaves of the two species of New Zealand flax, Phormium species (Hemerocallidaceae). It is also occasionally found on other plants with lilly-like leaves.

Adult females and nymphs have sucking mouthparts. Specially shaped rods called stylets are held in the short sheath-like rostrum. When it wishes to feed, the scale insect moves the tip of the rostrum onto the surface of the plant leaf. The stylets are then gradually pushed into the plant and manoeuvred into cells of the plant leaf. The stylets form two tubes, one down which saliva is pumped into plant cells and the second tube through which it sucks the contents of the plant cells. The dead plant cells turn yellow and the yellow patches of dead cells can be seen on the upper side of plant leaves. Unlike other scale insects they have a blind gut, no join between the stomach and anal opening, so unlike many other scale insects, they cannot excrete honeydew.